When the publisher starts shipping again next month (they promised me that they will never charge more than $40), I recommend buying multiple copies so that you get more revenue during the next shortage.

Supply and Demand (in that order)

The basic tools of supply and demand help immensely to understand and predict everyday events in our world. These days, many of those events are related to the Redistribution Recession of 2008-9. But I also look at other issues related to fiscal policy, labor economics, and industrial organization.